The Long-term evolution (LTE) is a wireless standard which serves a large number of user equipments (UEs) and supports a wide range of bandwidths. The LTE standard uses a minimum bandwidth of 180 KHz for communication with the devices. In downlink (DL), the LTE uses orthogonal frequency division multiple access (OFDMA) and single-carrier FDMA (SC-FDMA) in uplink (UL).
In LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, known as evolved Node-Bs (eNBs), communicating with a plurality of user equipments (UEs). The plurality of UEs communicates with a base station (BS) or an eNB through the DL and the UL. Cell search and synchronization in the LTE system is performed by the UEs using both the Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS).
The dedicated channel for synchronization in LTE is further divided into two parts namely Primary Synchronization channel (PSCH) and Secondary synchronization channel (SSCH). The signals transmitted on PSCH and SSCH are Primary synchronization Sequence (PSS) which carry sector ID (SID) and Secondary synchronization sequence (SSS) which carry Group ID (GID) respectively. The BS ID is obtained by combining the IDs on PSS and SSS. In order to detect the BS ID, the UEs have to extract the information from both the synchronization channels properly.
Under the process of cell search, information including BS ID, timing and frequency related to the BS has to be acquired by the UEs. The BS ID identification operation is said to be completed once the UEs perform the actions such as acquisition of the symbol and frame timing, carrier frequency offset (CFO) estimation and extracting the BS ID. In order to perform these actions accurate synchronization of the channel is essential in both time and frequency domain.
In an existing method, synchronization of the channel is achieved through an estimator which makes use of pilots which are broadcasted periodically. The pseudo noise (PN) sequences are used as pilots to generate an orthogonal frequency division multiplexing (OFDM) symbol, whose first and second halves in time domain are identical (i.e., second half is replica of the first half). Assuming the channel is same in the two halves of the OFDM symbol, the auto-correlation of N=2 windows with its replica, provides the estimates of frame timing and frequency offsets. This method is however not adoptable, since the nature of the pilot structure which is entirely different. Further, applying this method between the two synchronization signals is also not viable because of the distance between channels, which are separated by 5 milli-seconds (msecs). The channel cannot be assumed to be unaltered for a period of 5 msecs.
In another existing method, a maximum-likelihood (ML) estimator is used for timing and fractional frequency offset (FFO) estimation using cyclic prefix (CP) present in each symbol. This is accomplished by the autocorrelation of CP with its replica in the symbol. The ML estimator is used to determine the coarse timing. For better estimates, this can be averaged over multiple symbols. However, the ML estimator is prone to the effects of the delay spread. In the ML estimator, the noise terms are present in both the correlating samples, yielding more noise terms in the product, since it is an auto-correlation on the received signal.
The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.